Can someone explain why some are banked and some aren't? What are the advantages and disadvantages?

Also, why are some tracks have 80 meter straightaways and 120 meter turns or vise versa? Why do this?

To make them faster. Some have 300 meter flat and they are the fastes. Some times schools dont have the money to make them banked

I'd say the banked turns have more of a benefit for sprinters then distance runners.

Just like on (car) race tracks, you have banked turns so it's possible to carry more speed through the corner.

Similarly, if the turns are longer, they aren't as tight. That also means you can apply more of the force to go forward rather than turning.

Give, have ya ever gotten the chance to run at Notre Dame's (South Bend. Indiana) indoor track?

"a six-lane track one fifth of a mile long - making it as large as any indoor track in the nation."

Thanks for the feedback.

Nope, never ran on Notre Dame's track. Sounds like a great track though. However, I doubt records are allowed there.